In plate rolling trains, a slab of defined length is rolled into a sheet in a plurality of passes by rollers. Because the slab is heated, reference is also made to a hot-rolled sheet or hot-rolled strip. For the purpose of rolling the hot-rolled sheet or hot-rolled strip, use is made of at least one rolling stand, through which the hot-rolled sheet or hot-rolled strip is moved back and forth until the required number of passes is reached, i.e. the desired thickness of the sheet is produced. This operation is also called reversing.
For hot-rolled strips, use is made in particular of Steckel mills comprising one or more rolling stands that are arranged between two coilers onto which the strip can be wound.
In this case, it is also common practice to provide two rolling stands, the first rolling stand being used for blooming and the second rolling stand for finish rolling. The hot-rolled sheet or hot-rolled strip is moved back and forth in both rolling stands.
This differs from a continuous production line, in which a metal strip is fed progressively through rolling stands which are arranged one after the other. At the end of a production line, the finished strip is wound onto so-called coils.
In order to allow automation in a rolling train, such that the desired target parameters of the sheet or strip (e.g. target thickness, width, etc.) are achieved as precisely as possible, the temperature distribution in the hot-rolled sheet or hot-rolled strip is determined at a specific location, e.g. using a model or by means of a temperature measurement, e.g. using a pyrometer. In this case, the temperature can be determined at a plurality of points on the hot-rolled sheet or hot-rolled strip, thereby ultimately producing a temperature distribution. A model of the plate rolling train and the hot-rolled sheet or hot-rolled strip is then used to determine work parameters of the individual train components, e.g. the descaling unit, cooling or heating devices and obviously the rolling stand, such that the desired sheet parameters are achieved in the context of desired material properties. In particular, the temperature influences of the individual components of the plate rolling train are taken into consideration here. As part of the so-called precalculation, the temperature of the hot-rolled sheet or hot-rolled strip is therefore determined at specific positions depending on the assumed future temperature influences, in particular at the action positions of the components of the plate rolling train, and the required parameters which must be used to control the components are determined therefrom.
Nevertheless, discrepancies occur during the actual rolling operation because it is not possible to calculate all influences perfectly in advance. It is therefore common practice during the rolling process to record and store operating parameters, e.g. sensor values, which represent a temperature influence. Tracking systems which allow tracking of each individual point of the hot-rolled sheet or hot-rolled strip are also well known. This information is routinely used to perform a postcalculation at the cited action positions, or shortly after or before or at other specific positions, using the actual operating parameters but the same model. This postcalculation provides a current temperature which is used as a basis for a new precalculation. In rare cases, it is also normal practice to perform a comparison between the current temperature and the precalculated temperature before a new precalculation, and only to perform a new precalculation in the case of a significant difference. In practice, however, evidence shows that discrepancies occur in most cases, and therefore a new precalculation for updating the work parameters is generally performed without prior comparison operations. A new precalculation of this type is frequently also called a recalculation.
Both the postcalculation based on the recorded operating parameters, which represent the temperature influences, and the recalculation require a non-negligible time that can extend into seconds. During this time, effective processing time is lost for the hot-rolled sheet or hot-rolled strip, which is also standing still and will automatically continue to cool. In addition, significant computing power is required for the postprocessing and the new preprocessing.
Although only the temperature of the hot-rolled sheet or hot-rolled strip has been mentioned so far, this is merely one of a plurality of state variables which in effect describe the state of the hot-rolled sheet or hot-rolled strip. Equally relevant for the processing properties are e.g. the phase distribution, the residual work-hardness or grain sizes, this likewise can be established using models and suitable measurements.